In traditional metal alloy production, the ingredients for making a predetermined composition of metal are introduced to a furnace such as a basic oxygen furnace or an electric arc furnace, in which the constituents liquify and mix to form a molten metal pour. A layer of slag including impurities and catalysts is carried at the top of the molten metal layer. The molten metal is then discharged to a ladle for transport to an intermediate processing station or another production facility such as strand or sheet processing. At the production facility, the metal is discharged from the ladle to a vessel such as a tundish. While the processing stations may be provided with heat sources to maintain a liquid mixture once the pour has reached the processing destination, a substantial amount of heat was lost from the previously known open-topped ladles.
In order to address energy conservation concerns, it has been found to be useful to enclose the ladles during the transporting of molten metal from the furnaces to the processing equipment and during processing. Moreover, another recent innovation has been to enhance the metallurgical composition of the pour by adding metallurgical enhancements to the slag layer or the molten metal while heat energy is being maintained or adjusted in the ladle. Unfortunately, while closure of the ladle chamber permits metallurgical enhancement even during transport of molten metal from the furnace to a processing station or production facility, the prolonged period of the processing conditions, including heat and inaccessibility, does not permit previously known pour control techniques to be employed with success in these vessels.
For example, previously known techniques for controlling discharge from the vessel wherein a refractory plug is positioned and lowered over the nozzle by mechanical arms, as in a stationary furnace, cannot be employed with the closed vessels. Moreover, previously known refractory bodies such as that taught in U.S. Pat. No. 4,601,415 to Koffron cannot be introduced into a closed vessel when the level of molten metal in the vessel approaches the critical level at which a vortex forms over the discharge nozzle. Moreover, the previous refractory bodies formed with a specific gravity designed solely so that they are buoyantly supported in the melt may deteriorate rapidly under prolonged exposure to the ladle conditions and could not complete their intended function under prolonged contact with the molten metal and the slag layer interface.